Magneto-optical garnets for integrated optoelectronic devices

One of the efforts of integrated optics is the integration of macroscopic optical components such as an optical isolator on a single chip. Therefore magneto-optically active materials with high Faraday rotations are needed. Bismuth iron garnet (BIG) Bi3Fe5O12 is known for its high Faraday rotation at room temperature, but it forms in a non-thermodynamic way and only grows on garnet substrates like gadolinium gallium garnet (GGG) Gd3Ga5O12. Our ambition was to investigate the possibility of depositing such an integrated optical device based on magneto-optical BIG. A general overview of our extensive fundamental research is given in this paper. We first analysed the growth mechanisms of BIG on GGG, especially the nucleation process and the film growth which are important for BIG film synthesis. Then we worked on a garnet buffer system to enable film formation on other substrate materials like silicon or fused silica. To obtain the optical constants of the deposited material, a fitting algorithm was implemented. It calculates the optical properties of material stacks from transmission measurements. Furthermore, we wanted to vary the lattice constants of the garnets for a better adaption to the substrates. Because different rare earth elements have different atomic radii, it should be possible to vary the lattice constant by incorporating these atoms in the crystal. Therefore a number of rare earth doped garnets were produced and their film properties were analysed. During the buffer development we found an oscillatory effect in the Faraday rotation, which was examined in detail.